Developing and testing integrated circuit (IC) devices, also referred to as semiconductor devices, involves designing, manufacturing and testing these devices according to desired operating parameters. Quality assurance has been a concern in the development, fabrication and testing of IC devices, but is particularly important as these devices become ever more complex.
As IC devices have evolved from two-dimensional (2D) to three-dimensional (3D) structures, quality assurance methods are evolved as well. The quality assurance process is also referred to as “metrology.” Older metrologies used at the 2D level include using a critical dimension scanning electron microscope (CDSEM) to analyze 2D structures formed according to a particular design and manufacturing process.
Currently, scatterometry (a type of optical-based metrology also referred to as optical critical dimension, or OCD) is being used as a metrology technique for 3D or other complex IC structures. Scatterometry involves propelling light at an IC structure (e.g., a device, array and/or chip, which may be at a nanometer (nm) scale) and detecting how that light scatters. The manner in which the light scatters indicates the quality (dimensions) of the IC structure as compared to a desired model. Scatterometry can help to identify issues between layers of a structure, as well as within or between buried devices or objects in a structure. Scatterometry is an attractive metrology for a number of reasons, one of which is that it is generally non-destructive. That is, the IC structure tested via scatterometry need not be discarded after testing (as in older metrologies). Scatterometry also allows for high throughput, meaning that a large number of structures can be tested within a short period of time.
The term “model-based metrology” refers to the conventional process of using scatterometry by building a model of how an expected IC structure scatter the light, and comparing the measured scatterometry data to that model. The model is essentially a database that includes a variety of diffraction signatures for the 3D structure. However, the model-based nature of scatterometry means that this approach is highly model and structure dependent, with a very long lead-time. Being model-based, conventional scatterometry relies upon providing and updating a large database with information about dimensions and parameters of IC structures.